Woodland ponds, temporary pools and damp ground are important for many invertebrates and amphibians, as well as for bats and other creatures. They may also contain a specialised flora.
Some ponds are very stable, changing little over long periods of time. Other ponds tend to silt up with the accumulation of marginal vegetation, decaying organic matter and soil that washes into the pond. As long as they are not polluted, all ponds in all stages have ecological value, and intervention is not necessary. Each stage, from open water, through silted pond, muddy hollow to dry ground will have wildlife interest. It may be better to create several ponds, at different stages in the succession, than to try to intervene and keep one pond at a particular stage in the succession.
Intervention in the natural development of a pond should only take place if the pond will otherwise be lost, and cannot be replaced by creating a new pond nearby. If intervention is necessary, no more than one quarter of the marginal vegetation, sediment or trees should be removed in a five year period.
Ponds which have not been disturbed for 50 years or more will contain sediments which can give important insights into past vegetation and land management. They may also contain interesting artefacts which have been preserved in the anaerobic conditions. Old sluices, artificial linings and other parts of the pond’s structure are of archaeological interest, and should not be disturbed. Contact the local authority archaeologist for advice before disturbing an old pond. See The Pond Book (1999) for further details on the historical value of ponds.
Note the following:
- Sunny ponds and other wetland areas support a more diverse flora and fauna than similar areas under shade, but this does not mean that shaded ponds are valueless. Shady ponds can support populations of specialised invertebrates and other creatures, which occur nowhere else.
- Ponds which are shaded by mature or veteran trees have been shaded for a century or more, and represent a stable habitat which should not be altered by clearance or felling. Ponds which are shaded by young growth are more likely to benefit from some clearance.
- Branches and other rotting wood in ponds and wet ground are substrates for algae and fungi, and provide egg-laying sites for dragonflies and food for aquatic fly and beetle larvae. Rotting willow exudes tannins into the water which help prevent algal blooms, acting in the same way as barley straw. Tidying-up operations may therefore be misguided.
- Temporary pools which dry out in summer are a valuable habitat for certain invertebrates, and should not be altered in an attempt to make them hold water all year. Ruts created by vehicles and ground trampled or ‘poached’ by stock can create small pools of stagnant water which are valuable to some invertebrates.
- Shallow pools, less than 1m (3’) deep, are much more valuable for wildlife than deeper pools. For invertebrates and amphibians, the important part of any pond is the shallow margins. Deep open water which does not become overgrown with plants by midsummer is the least valuable. Ponds which appear ‘choked’ with vegetation by mid summer are not necessarily so.
- Muddy pond margins and bare shingle are important habitats for invertebrates, and should not necessarily be vegetated. Bare ground at pond edges can usefully be maintained by trampling of people or animals, although excessive trampling all around the pond may be destructive.
- Where ponds fed by ditches tend to rapidly silt up with runoff from nearby fields or roads, then a silt trap is worth constructing to allow easy removal of the silt before it reaches the pond. This will also reduce nutrient enrichment from agricultural run-off, which is damaging to pond habitats.
- As an alternative to the silt trap shown above, a simple feeder pond can be dug, in which the water collects before it flows into the pond. This feeder pond can then be cleaned as necessary by hand or digger to remove the trapped silt. Where the runoff is polluted, a balancing pond or reedbed can be constructed and planted with common reed (Phragmites communis). This will help absorb and lock up any pollutants, and provide an unpolluted water supply to the wildlife pond. See Waterways and Wetlands – Wetlands for water treatment for further details.
- Before clearing growth to reduce shading of a pond, assess the value of the species involved. Alder and willow, which thrive around ponds and in other damp locations are especially valuable for the many organisms they support, and should normally not be removed.
- The surrounds of many ponds have been altered in the past by the planting of exotic species such as bamboo and rhododendron. Other exotic species may have spread unintentionally, including the very invasive Japanese knotweed. Clearance of these species is not easy as they all regrow strongly from the stumps or roots. See here for advice on control.
- When planning clearance, consider the effect of the sun and wind. Concentrate any clearance on the south side, where it will have most effect in increasing light to the pond. Don’t remove growth which acts as a shelter from prevailing winds.
- Where removal of marginal vegetation and silt is necessary, do the work in September or October to minimise adverse effects on pond wildlife. Marginal vegetation can either be removed in sections on an annual or longer rotation, or by clearing from the ‘invading front’. On larger ponds both approaches can be used in different parts of the same pond.
- Deposit the spoil where it can’t wash back into the pond, and where it will not smother valuable ground flora. If necessary remove it from the site.
Springs and streams
Natural springs and seepages occur as a result of geology and landform, and as such may have remained unaltered for thousands of years. Those in woodlands at a distance from habitation or remnants of industrial activity are likely to be the least affected by human activity. The invertebrate fauna associated with these springs and pools may be very specialised, and no attempt should be made to alter the flow by damming or digging.
Streams which run through shady woodland have constant cool conditions, and can support a different fauna from those which run through open ground, where water temperatures will fluctuate. Like ponds, it is therefore not necessary to clear away all shading vegetation, but to leave a variety of streamside habitats. Where new woodland is being created in an area which includes a stream or pond, the margins should be left unplanted, so that conditions in the water and along its margins are changed as little as possible by the new woodland.
